It is well known that certain electronic components, in particular of the active type, give off high levels of heat energy when they operate at high power. Such components are commonly associated with heatsinks designed to dissipate the heat energy given off by the components, so as to carry away the heat dissipated thereby and thus to lengthen the lives thereof. In general, the heat energy originates from the chips in the active components, and the packages (usually made of metal) containing the components are not capable of carrying away all of the heat energy. That is why thermal contact is made between the electronic components to be cooled and a wall of a heatsink (also referred to as a "dissipator"). FIG. 1 shows such a heatsink against which an electronic component is fixed.
In FIG. 1, a component 10 is pressed against a sidewall 11 of a heatsink 12. For example, the component 10 is a power transistor and its three connection pins are soldered to a printed circuit board 13. The heatsink 12 is also fixed to the printed circuit board 13 by means that are not shown. The heatsink 12 is constituted by an aluminum extrusion and has a plurality of fins 14 for dissipating the heat energy given off by the component 10.
The heat from the electronic component is dissipated well if the fixing means for fixing the component 10 on the wall 11 exerts sufficient pressure on the component thereon. The purpose of the pressure is to establish good thermal contact between the wall and the component, and the quality of the thermal coupling between the package containing the component and the heatsink is dependent on the magnitude of the pressure. Furthermore, in numerous applications, it is necessary for the component 10 to be electrically insulated from the heatsink 12 so as to avoid electrical short-circuits between various metal packages containing components and not having the same potential, and between the heatsink itself and the component 10.
Different means may be used to fix the component against the heatsink, and in particular the component may be fixed against a sidewall of the heatsink by means of a screw. In that technique, which is widely used, an insulating piece disposed in a recess provided in the component 10 prevents electrical contact from being made between the orifice (which is in general metal) and the heatsink via the screw. An insulating sheet, e.g. made of mica, is placed between the component and the heatsink. The main drawback of that fixing method is that it is difficult to implement when the insulation distances required between the component and the heatsink are large.
Moreover, that method involves machining the heatsink (boring a recess) in a direction that is perpendicular to the bores already machined in the heatsink for fixing it to the printed circuit board. For example, such bores enable the heatsink to be mounted on small vertical columns. It is inconvenient to have to machine along different axes because the heatsink then needs to be turned over. This is particularly inconvenient when the machines used (programmed numerically controlled machines) have only limited machining possibilities, e.g. in only one direction.
It is possible to machine in only one direction provided that the component can be fixed under the heatsink. The legs of the component must then be bent at 90.degree. so that they can be soldered to the printed circuit board, and this complicates mounting considerably. Moreover, the orifice for fixing a component by means of a screw must be tapped, which is time-consuming, or else a nut and a locknut must be used to co-operate with the screw. Mounting a component on the heatsink is then more complex and also takes a long time. Finally, that technique can only be used with electronic components that have through holes for screws, and it cannot therefore be used with all types of components to be cooled.
Another solution is to press the component against a wall of the heatsink by means of a fixing clip, as shown in FIG. 2. FIG. 2 is a side view of a fixing clip 20 whose top end is held inside a cutout 21 provided in the sidewall 11 of the heatsink 12. The cutout 21 made either during extrusion, or by machining, is substantially rectangular in shape and has an opening in the sidewall 11, through which opening the body of the clip 20 can pass. The body of the clip 20 has a certain amount of resilience making it act as a spring, whereby a force F can be exerted on the component 10. The bottom end of the clip 20 is thus pressed against the front face of the component 10. A sheet of insulating material, e.g. made of mica, may be inserted between the rear face of the component 10 and the front face 11 of the heatsink 12.
That embodiment offers the advantage that it can be applied to any component to be cooled by means of the heatsink because the component needs no orifice. The components may, in particular, have different shapes.
However, machining the cutout 21 is complex to perform and therefore costly, and the same applies to the fixing clip 20. Furthermore, considerable machining is required, and, as a result, a large amount of matter is removed. Therefore, the heat removal qualities of the heatsink are reduced. Moreover, the only way to mount the clip 20 is to engage one of its ends in the cutout 21, and other clips serving to fix other components may obstruct the path of said clip. Finally, to obtain the cutout 21, it is advisable to make the design of the heatsink specific, thereby preventing many of the standard heatsinks on the market from being used.
An object of the present invention is to mitigate those drawbacks.
More precisely, an object of the invention is to provide a fixing device for fixing an electronic component against a wall of a heatsink, the fixing device providing optimum thermal contact between the component and the heatsink while also having a simple structure, being cheap, and being easy to adapt to the heatsink. The fixing device must therefore exert pressure on the component to press it against the heatsink so as to enhance heat transfer.
Another object of the invention is to provide such a fixing device that only requires limited machining of the heatsink.